In Poland, ticket controllers (commonly known as “kontrolerzy biletów or simply kanary” in day-to-day Polish) play an essential role in maintaining the public transportation system.
Controllers are responsible for checking whether passengers have valid tickets. They aim to prevent fare evasion and ensure the financial sustainability of public transportation services. So make sure that you validate your ticket from the validation machines looks like in the picture.
In case of you are missing a ticket for the ride or your ticket was not validated. The controller has a right to fine you. These fines differ in each city.
Generally more than 100 zloties ≈ >23.31 € / ≈ >24.47 $